Mussel Strength: How Mussels Cling to Surfaces

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When mussels dangle from marine surfaces, they hold on by a
cluster of fine threads. These filaments may appear flimsy, but
they can actually withstand powerful impacts from currents or
crashing waves. Now, researchers are unraveling the secret of
these thin, bungeelike cords in order to develop more effective
glues and other synthetic biomedical materials.

Unlike barnacles, which fasten themselves tightly to rocks or
piers,
mussels use silky fibers, called byssus threads, to loosely
attach to a surface while still being able to drift and absorb
nutrients in the water. So, how do these seemingly delicate
threads help mussels stay put?

From laboratory tests and computer models, scientists at the
Massachusetts Institute of Technology (MIT) discovered that
roughly 80 percent of the length of byssus threads — the same
parts of the threads that connect the mussel to a hard surface on
one end — is composed of stiff material, whereas the remaining 20
percent, at the end that is affixed to the mussel itself, is soft
and stretchy. The combination of these different material
properties likely helps the
mussels adhere to surfaces, and enables them to survive the
impact of various forces. [ Photos:
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"It turns out that the … 20 percent of softer, more extensible
material is critical for mussel adhesion,” Zhao Qin, a research
scientist at MIT, said in a statement.

Researchers have studied byssus threads before, but Qin and his
colleagues wanted to observe how these threads, and all their
connecting parts, operate in simulated wave
conditions.

"We figured there must be something else going on," Markus
Buehler, head of MIT's department of civil and environmental
engineering, said in a statement. "The adhesive is strong, but
it's not sufficient."

The researchers placed an underwater cage in Boston Harbor for
three weeks to see how mussels attached themselves to glass,
ceramic, wood and clay surfaces. In the lab, the scientists used
a tensile machine to test the strength of byssus threads as they
were pulled and deformed.

Even though byssus threads have both stiff and stretchy
properties, the filaments are made of a protein closely related
to collagen, the researchers said. From their experiments, the
scientists discovered that the distribution of stiffness along
the threads is critical to their effectiveness.

Understanding how byssus threads work could help scientists
design synthetic materials with similarly flexible properties,
such as surgical stitches that connect tissues together. The
findings could also help in the development of new building
materials, sensors for underwater vehicles and other equipment
that could be subjected to extreme conditions, the researchers
said.

The detailed findings of the study were published online today
(July 23) in the journal Nature Communications.